Whatever the OEM calls for. But keep in mind "tinnerman" is a brand with different types (U, J, etc) that can also require different type fasteners: machine screws, AB fine thread sheetmetal screws, etc.
Regrettably, I seem to lack the C140A parts manual to Aircraft Spruce decoder ring; I presume "PK76X2-8-6" = truss head #8 x 3/8", but it doesn't specify A or B.
The PK76 was the brand name designator and may have indicated the A or B. But you're correct on the #8 screw and the length is usually in 1/16ths" so the 3/8" is good too. As to the thread differences, yes there is a difference between the A and B but the main issue was if a type AB screw/nut was used as it was fine threads. And they did make speed nuts for type A as well. An easier hack is to find a vender who makes screw kits for your 140 and see what type screw they include in the kits as it will usually be the best option for availability and cost. And for reference, the AN spec reference has been retired and most hardware is now classified under MS and NAS.
True, though Aircraft Spruce seems to use AN and MS numbers interchangeably. Sometimes if you type in an AN number to order you'll see the equivalent MS in your cart instead, or vice versa.
But you need to know while MS and NAS can substitute AN, the reverse is not true in all cases. So if the parts manual shows a MS or NAS item you cannot substitute the AN item UNLESS the aircraft original configuration was certified with AN. With the OEMs revising their manuals to the MS/NAS standards it gives the impression AN is no longer permitted to use. And since there is a mountain of NOS AN hardware in the world, it has created some confusion for your average aviator when trying to replace hardware. The main issues are cost in some cases and if a person specifically orders an MS or NAS item and the vendor gives you an AN instead. For example, have found AN hardware installed in shoulder harness mounts that are required to use MS hardware due to the load factor. The vender sent AN vs MS and the installer didn't think twice on installing it.
Oh yes, you guys with non-experimentals have all those silly rules...
Ha. But no silly rules to follow on this one. Simply basic physics which apply to E/ABs too. For example, the reason the substitution route for bolts is AN>MS>NAS>20 Series and not the reverse is all about tensile strength and not any rule. There are exceptions within the AN/MS/NAS specifications, but to assume those bolts are all unchangeable usually will prove you wrong in an unfortunate way if you make the wrong substitution. And even on an E/AB.Oh yes, you guys with non-experimentals have all those silly rules...
Of course, when the application requires a higher strength fastener you must use it. I was thinking more of the many cases where the strength is identical but the manufacturer uses the newer spec. Any time a substitution is made you must of course verify it's appropriate, but at least with experimentals you're allowed to do it. And I was being a bit facetious, of course. Most experimentals (all I've encountered) use the older specs anyway.Ha. But no silly rules to follow on this one. Simply basic physics which apply to E/ABs too. For example, the reason the substitution route for bolts is AN>MS>NAS>20 Series and not the reverse is all about tensile strength and not any rule. There are exceptions within the AN/MS/NAS specifications, but to assume those bolts are all unchangeable usually will prove you wrong in an unfortunate way if you make the wrong substitution. And even on an E/AB.
In general, it is correct when you compare at specification level. You’ll also find the AN, MS, and NAS specs were all around during the same time period with the govt maintaining the AN/MS spec and the industry the NAS spec. So there really wasn’t a changing of the guard on the spec side. However, the specification side went through a huge renaissance in the 1980s which upended everything and created a lot of confusion on both the civil and military side as to which spec was valid on what aircraft.
Just when I thought it was safe to back into the water... Thanks for posting - I would have never thought is would make a difference.
Most people forget to apply some type of film lubricant to the SS hardware when reinstalling it, and it subsequently galls and becomes a tough and damaging removal the next time. Few people understand that removing and installing screws and bolts and nuts with power tools, will turn the item fast enough to generate enough heat to remove any lubricant that was on the item. Even with a speed handle, one can get a fastener hot enough to make the lubricant go away, even on steel and cres hardware.
When used properly with a plastic washer/separator, should be fine. One of our club's planes has stainless steel camlocks for the aluminum cowl. It's properly designed not to have the stainless steel in contact / touching the aluminum.
That's why you put anti-seize on the stainless screws that are screwed into the aluminum mast on your sailboat.
As mentioned in the attached thread, its no problem especially when you don’t allow an electrolyte to remain in the same area which is needed for any corrosion to form. And aluminum washers, plastic washers, and even paint are all acceptable preventative barriers as well. As long as you keep your aircraft clean and maintained it shouldn’t be a problem and give you a better product. Just don’t try and paint the SS screws.
Funny you should ask. When replacing my taxi light, I found a mix of type A and type B, some of them rusty. Not sure if the zinc plating wore off or if it was non-aviation hardware to begin with. I ordered a bunch of SS type B to replace them.
Dan Thomas said:
Landing light stuff might be OK. The cowl may work loose as the cowl tries to shift and inflate (due to the air pressure in it) and the nylon compresses. Cessna has specified nylon washers under spinner screw heads to protect the spinner.